1. Field of the Invention
This invention relates to a camera being capable of simultaneously imaging scenes respectively seen in a plurality of directions and to an apparatus for visual recognition of surroundings of a vehicle, which uses such a camera.
2. Description of the Related Art
FIG. 10 is a diagram illustrating an operation of a vehicle equipped with a conventional apparatus for visual recognition of surroundings of a vehicle.
Generally, when a motor vehicle 30 is about to come in an intersection, a region indicated by oblique lines in FIG. 10 becomes a driver's blind spot 32. Further, the driver cannot visually recognize other motor vehicles 31 that are present in left-side and right-side blind spots 32, respectively, as viewed in this figure.
Thus, to enable the driver to visually recognize the condition of the dead spot 32, there has been put to actual or practical use an apparatus for visual recognition of surroundings of the motor vehicle, in which a camera 50 is mounted on the front cover thereof and images of the left-side and right-side blind spots 32 are simultaneously taken by the camera 50 and thus the images of the blind spots 32 are displayed on the screen of a monitor television 40 as shown in FIG. 11.
Next, an example of the conventional camera will be described hereinbelow with reference to FIG. 12.
Outer casing 4 serving as a housing is provided with entrance windows 4a and 4b in the left and right side portions thereof, respectively, so that extraneous light coming from the right and left can be incident thereon. Further, an image formation lens 3 is mounted in the outer casing 4. Image pickup device 6 constituted by CCD is placed at a focal point of the image formation lens 3. Moreover, a pair of first mirrors 18a and 18b are disposed at the left and right sides of the image formation lens 3, respectively. Furthermore, a pair of second mirrors 19a and 19b are placed in such a manner as to face the first mirrors 18a and 18b, respectively.
In the case of a camera 50 configured in this manner, extraneous light 5a coming from the right (namely, from above as viewed in FIG. 12) is incident on the outer casing 4 through the entrance window 4a. First, the extraneous light 5a is reflected by the first mirror 18a. Subsequently, the extraneous light 5a is further reflected by the second mirror 19a. Then., the extraneous light 5a reflected by this second mirror 19a is led to the image formation lens 3, so that an inverted (or vertically-flipped) normal image is formed on the left-side half of an imaging plane (namely, an image pickup plane) of the image pickup device 6.
On the other hand, the extraneous light 5b coming from the left (namely, from below as viewed in FIG. 12) is incident on the outer casing 4 through the entrance window 4b. Then, the extraneous light 5b is first reflected by a first mirror 18b. Subsequently, the extraneous light 5b is further reflected by the second mirror 19b. The extraneous light 5b reflected by this second mirror 19b is led to the image formation lens 3, so that an inverted normal image is formed on a right half of the imaging plane of the image pickup device 6.
Thus, this camera 50 is applied to an apparatus for visual recognition of surroundings of a vehicle, a picture signal representing an inverted normal image, which is formed from light received by the image pickup device 6, is displayed on the screen of the monitor television 40 so that a scene, whose image is taken, is displayed in such a way as to be upside down. Thus, as illustrated in FIG. 11, a normal image formed from the extraneous light 5a coming from the right is displayed on the right-hand part of the screen of the monitor television 40. Further, another normal image formed from the extraneous light 5b coming from the left is displayed on the left-hand part of the screen of the monitor television 40. Thus, the driver can check the conditions of the left and right blind spots 32 from the screen of the monitor television 40.
In the case of this camera 50, a normal image is obtained by reflecting the extraneous light 5a (or 5b) two times by means of the first and second mirrors 18a and 19a (or 18b and 19b) , namely, by changing an image, which is obtained as a mirror image by the first mirror 18a (or 18b), into the normal image by the use of the second mirror 19a (or 19b).
The conventional camera 50 is constructed as above described and thus can take (or shoot) images of regions respectively observed in a plurality of directions therefrom. However, the conventional camera 50 has a problem in that owing to the presence of the differences among illuminating angles of the sun or a lighting unit (namely, a luminaire), which respectively correspond to such regions, the image of the region corresponding to a certain direction is too bright, while that of the region corresponding to another direction is too dark.
Generally, in cameras, the luminance (brightness) of images of regions to be shot is controlled by diaphragm mechanisms or electronic shutters. Further, each of these diaphragm mechanisms and electronic shutters is operative to regulate the luminances of the entire images of such regions collectively. Thus, if these luminance control means are applied to the aforementioned camera 50, the luminances of the entire images of regions respectively corresponding to different directions are regulated collectively. Therefore, the camera 50 cannot solve the problem that the image of the region corresponding to a certain direction is too bright, while the image of the region corresponding to another direction is too dark.